Separation of phthalic isomers



United States Patent 3,198,173 SEl ARATION 0F ii-HTHALIC lfiQMERS PeterForts, Highland, ind, and Eliis K. Fields, Chicago, Eih, assignors toStandard (Bil Company, Chicago, IEL, a corporation of Indiana NoDrawing. Filed Dec. 3, 1959, Ser. No. 856,940 3 Claims. (Cl. 260--525)The present invention relates to a method of separating mixtures ofphthalic acid isomers, and further relates to the separation of mixturesof isophthalic acid and terephthalic acid by treating the mixture ofacids with a lithium halide and an oxygented organic solvent. Moreparticularly, the invention concerns a process for separating solidmixtures of isophthalic acid and terephthalic acid by contacting ortreating the mixture of acids with lithium bromide and an oxygenatedorganic solvent and separating resulting liquid and solid phases.

A common preparation of phthalic acids is by oxidizing the correspondingxylenes. For example, mixed petroleum xylenes containing metaandpara-xylenes may be oxidized to form a mixture of isophthalic andterephthalic acids. The phthalic acids are useful as reactants to formpolyester poiymers. Where polyesters are formed from a mixture ofphthalic acid isomers, the melting point of the polyester product issubstantially lower than it would be if the polyester were prepared froma substantially pure phthalic acid isomer. Further, the substantiallypure isomers polymerize or polyesterify more rapidly to form polyesters.Because of the desirable higher melting point of the polyester formedand because of the increased rate of polymerization orpolyesterification it is desirable to separate the phthalic acid isomersfor use in the polymerization or polyesterification reaction. It isapparent that either the xylene isomers should be separated beforeoxidation to form the acids or the acid isomers should be separatedafter oxidation. The xylene isomers occurring in the oxidation feed arediflicult to separate by conventional methods due to the closesimilarities of their physical properties. Therefore, as an alternative,it has been suggested to separate the mixed isophthalic and terephthalicacids produced by oxidation of mixed xylenes containing meta andpara-xylenes. However, the mere suggestion of making such a separationhas not been an answer in itself to the separation problem. Conventionalmethods of separation by fractional distillation and solvent extractionhave not been satisfactory. Fractional distillation is impracticalbecause of the tendency of terephthalic acid to sublime and because ofthe high boiling point of isophthalic acid which increases the danger ofthermal decomposition resulting in loss or contamination of the product.Solvent extractions have not been commercially attractive because ofdifficulties in finding a suitable solvent which will preferentiallydissolve one isomer with acceptable capacity and because of difficultiesin discovering extraction conditions which enhance solubility of oneisomer to achieve satisfactory capacities. Further, because of therelative insolubility of the metaand para-phthalic acids, workablesolvent extraction processes usually must be carried out at hightemperatures. As another separation scheme, it has been proposed toconvert the mixture of acid isomers to alkali metal salts and rely ondifferences in solubility of the salts in aqueous salt solutions forseparation. Such a procedure involves converting the acid isomers tosalts by reacting with an alkali metal hydroxide such as sodiumhydroxide and, after physical separation of the salts, dissociating thesalt with hydrochloric acid to free the separated isomer. However, thisprocedure necessitates the handling oflarge volumes of corrosive sodiumhydroxide and hydrochloric acid with increased costs in equipment forsuch handling, as well as 3,159,173 Patented Sept. 22, 1964 increasednecessity for more extensive safety precautions for protection of plantpersonnel. Further, the procedure expends about two moles each of thehydroxide and hydrochloric acid, an incurrence of cost which furtherdetracts from commercial attacriveness.

Broadly, we have now discovered that mixtures of isomers of a normallysolid phthalic acid may be separated by treating the mixtures of acidswith a lithium halide and an oxygen-containing organic solvent.Advantageously, such mixtures which may be separated contain a phthalicacid in which the carbonyl groups are separated by at least three ringcarbon atoms. Two isomers of such configuration may be separated fromeach other or from another isomer. Particularly, we have discovered thatmixtures containing isophthalic and terephthalic acids can be separatedby contacting with lithium bromide and an oxygen-containing organicsolvent and separating resulting complexes as liquid and solid phases.The present separation process is advantageous in that it is capable ofgiving relatively good yields of high purity acid isomers. Anotheradvantage of the process is that it may be carried out at lowtemperatures, for example, below about C. A further advantage of thepresent separation process is that it eliminates the necessity andexpense of handling and expending large amounts of highly corrosivefluids.

In accordance with our invention, a mixture containing terephthalic andisophthalic acids is treated with a solution of at least about oneweight percent and preferably 10 to 30 weight percent of a lithiumhalide, such as, for example lithium bromide, in a suitable solvent,e.g., an oxygencontaining organic solvent, advantageously at a temperature in the range of from about '20 C. to about 100 C. and preferablyfrom about 0 C. to about 40 C. The contacted mixture may be agitatedslightly to mix the acid isomers and lithium halide solution and may bethen allowed to stand for a short period of time to precipitate a solidphase having an increased tercphthalic content leaving a separate liquidphase having increased isophthalic acid content. The two phases areseparated from each other by known separation methods such as byfiltration,

decanting, or the like. The terephthalic acid product may be washed witha solvent such as, for example, water to remove lithium halide. Theterephthalic acid may be treated again with a lithium halide solutionfor further purification. The lithium halide solution components may beremoved from the liquid phase leaving a solid isopthalic acid producthaving an increased isophthalic acid content. The isophthalic acidproduct may also be further separated by treating again with a lithiumhalide solution.

Although any lithium halide may be used in this invention, e.g. lithiumbromide, lithium chloride, lithium iodide and lithium fluoride, theparticularly preferred lithium halide is lithium bromide. Hereinafter,the lithium halide will be referred to as lithium bromidepbut it is tobe understood that any such lithium halide is intended where lithiumbromide is mentioned.

The removal of the lithium bromide solution components from theliquidphase may be by evaporation or distillation to remove oxygen-containingorganic solvent followed by extraction of the resulting residue from thedistillation with an aqueous or other solvent for lithium bromide andfiltration to recover the solid isophthalic The lithis substantiallyinsoluble.

as often as desired; however, we have found that only one removaloperation is necessary if sutficient solvent for the lithium bromide isused. In all cases above, the aqueous solvent or odaer solvent forlithium bromide may be any solvent boiling below about 250 to 300 C. inwhich'lithium bromide is substantially soluble and in which theparticular phthalic acid isomer to be washed Lithium bromide may berecovered from the aqueous solvent or other solvent in reuseable form byevaporating the aqueous or other solvent.

.Examples of suitable oxygen-containing solvents are those containingonly carbon, hydrogen and oxygen, such as the low molecular weightketones, alcohols, ethers, and esters normally used as solvents andpreferably those containing from about 2 to about 12 carbon atoms. Thesolvent must be capable of dissolving or solubilizing at least about 2weight percent of lithium bromide based on the solvent to form asolution of lithium bromide in oxygen-containing organic solvent. Asimple experiment which may be used for determining a suitable solventis as follows: add at least 1 gram of dried lithium bromide to 15 ml. ofsolvent; agitate the mixture; let the mixture .stand for about thirtyminutes; filter and collect and dry the lithium bromide from theprecipitate. If the difference in weight between the collected lithiumbromide and the original lithium bromide is greater than about 0.24gram, at least that amount of lithium bromide has been solubilized bythe 15 ml. of solvent and the solvent acetate, ethylene glycol monoethylether acetate, etc., and

the like. Particularly preferred are acetone, methyl ethyl ketone, andethyl ether.

The lithium bromide solution in oxygen-containing organic solventcontains at least about one weight percent of lithium bromide. Thesolubility of lithium bromide sets the higher limit on the concentrationof lithium bromide dissolved in solvent; however, it is preferred to useat least about 10 weight percent lithium bromide and no more than aboutweight percent lithium bromide based on solvent. For maximum etliciencyin utilizing lithium bromideythe solvent should be present in theextraction mixture in amounts exceeding about 60 weight percent based onsoluble acid so that sufficient solvent is present to accommodate thesoluble acid. Increasing the amount of solvent used in the extraction,with respect to a constant given amount of lithium bromide and aconstant given feed material containing the acid isomers, generallyresults in increased yield in the extract (soluble acids) and decreasedyield in the raflinate (insoluble acids) with no substantial effect onselectivity in either phase. Increasing total lithium bromide content ina constant amount of solvent in separating a given feed materialgenerally results in increased extract yield and decreased selectivityfor isophthalic acid (soluble acid) in the extract. Conversely,increased total lithium bromide content generally decreases yield ofraifinate and increases purity of terephthalic acid in the raffinate.Further, an increased amount of lithium bromide solution at agivenconcentration on a given feed generally increases total yield ofsoluble isophthalic acid in the extract while selectivity remains aboutthe same, and also tends to decrease yield of raffinate while increasingpurity of the insolublev terephthalic acid in the raflinate. The abovegeneralities regarding the separation process are based on our studiesof the separation phenomena. The

total amount of lithium bromide solution which should he used forpreferred and optimum results with regard to a given feed material willbe at least about 4 moles of lithium bromide per mole of isophthalicacid and will be discussed further below in connection with our proposedtheory of the separation phenomena which results from our process.

The lithium bromide used in preparing the above solution is non-aqueous.Lithium bromide is hygroscopic, and although the wet lithium bromide isoperable in this invention, it is preferred to use a dried lithiumbromide since the dried salt apparently enhances the separation.

As a typical example of the process of this invention, the effluentslurry from an oxidation of petroleum-derived mixed xylenes (containingabout one part by volume each of ortho-xylene, para-xylene, and ethylbenzene and two parts by volume of metaxylene) is washed with aceticacid to remove benzoic acid and orthophthalic acid and is then chargedto a separator equipped with an agitator and filtered effluent line. Thesolids are deposited in the separator and the slurry liquid is removedby the filter line. A 4 weight percent solution of lithium bromide inmethyl ethyl ketone is added in suflicient amounts to provide at leastabout 4 moles of lithium bromide per mole of isophthalic acid. Theagitator is started momentarily to mix the solids and lithium bromidesolution. The mixture is allowed to stand for 30 minutes and the liquidphase is removed by the filter line and recovered. The liquid phase isdistilled at about 135 F. to remove the solvent for reuse, and theresulting residue is then washed with two gallons of water per pound ofresidue to remove lithium bromide in the wash fluid. The wash fluid isremoved by filtration and the filtered product contains a substantiallyincreased percentage of isophthalic acid in comparison with the originalfeed material. The solid phase is recovered from the separator andwashed with one gallon of water per pound of solid phase to remove anyentrained lithium bromide. The washed solid phase is recovered from thewater wash by filtration as a product having substantially increasedterephthalic acid content.

The following examples are for the purpose of illustrating the processof this invention:

EXAMPLE I As an example of separation by this invention, a solu tion of1.0 g. of dried lithium bromide in 15 ml. of acetone was added to a 50ml. stoppered flask containing 0.5 g. of a 50-50 mixture of isophthalicacid and terephthalic acid at room temperature (25 C.). The resultingextraction mixture was agitated and then allowed to stand for 30minutes. Undissolved acid was recovered by filtration as a solidraflinate and weighed 0.25 g.

Ultraviolet analyses of the solid raflinate were as follows: 1

Mol percent Isophthalic acid 1.3

Terephthalic acid 98.1

Orthophthalic acid 0.6

All results reported in this example and in other ex amples hereinafterhave been normalized to total phthalic acid isomers.

.very little, if any, solubility in the acetone.

EXAMPLE n As an example demonstrating recovery of the dissolved acid inthe filtrate asolution of 1.0 g. of dried lithium bromide in 30 ml. ofacetone was added to a 50 ml. stoppered flask containing 2.0 g. of a50-50 mixture of isophthalic acid and terephthalic acid at roomtemperature (25 C.). The resulting extraction mixture was agitated andthen allowed to stand for thirty minutes. Undissolved acid was recoveredby filtration as a solid rafiinate and weighed 1.5 g. The extract(filtrate) was evaporated to dryness leaving a solid residue. The solidresidue was washed with ml. of water and filtered to recover the solidresidue. The recovered solid residue weighed 0.75 g. Ultravioletanalyses of the solid rafiinate and the washed solid residue from theextract (filtrate) were as follows:

Iso- Tcreph- Orthophthalie thalic phthalic acid, mol acid, mol acid, moipercent percent percent Solid raiiinatc 17. 9 82. 0 0. 1 Solid residuefrom extract 92. 8 7. 2

EXAMPLE 111 As an example illustrating recovery of product from the washwater, a solution of 1.2 g. of dried lithium brophthalic acid andterephthalic acid at room temperature (3.). The resulting extractionmixture was agitated and then allowed to stand for minutes. Undissolvedacid was recovered by filtration as a solid raffinate and weighed 1.35g. The extract (filtrate) was evaporated to dryness leaving a solidresidue. The solid residue was washed with ml. of water and filtered torecover the solid residue. The recovered solid residue weighed 0.58 g.The wash water used above was saved and evaporated to dryness leaving awash water residue weighing 0.05.

ltraviolet analyses of the solid railinate, the washed solid residuefrom the extract (filtrate) and the wash water residue were as follows:

ii The recovered solid residue weighed .87 g. Ultraviolet analyses ofthe solid rafiinate and the solid residue for isophthalic, terephthalicand orthophthalic acids were as follows:

Iso- Toroph- Orthophthalic tha-lic phthalic acid, mol acid, Incl acid,mol percent percent percent Solid raliinate 4. 5 95. 5 Solid residue 92.1 7. 5 0. 4

Mol percent Isophthalic acid 94.5 Terephthalic acid 4.8 Orthophthalicacid 0.7

EXAMPLES V TO IX In order to determine the effect on the extraction ofthe lithium bromide concentration, a series of examples were run asfollows: For each example, a solution of the amount of dried lithiumbromide in 15 ml. (12 grams) of acetone was added to a 50 ml. stopperedflask containing 2 g. of a 50-50 mixture of isophthalic acid andterephthalic acid. The resulting extraction mixture was agitated andthen allowed to stand for about thirty minutes. Undissolved acid wasrecovered by filtration as a solid rafiinate and the weight of solidraffinate from each example is recorded in Table I. The extract(filtrate) was evaporated to dryness leaving a solid residue. The solidresidue was washed with about ten m1. of water and filf gfigai tered torecover the solid residue. The weight of each acid, mol acid,m0l acid,moi recovered solid residue is reported in Table I. Ultraviolet percentpercent pmcn" analyses of the feed, the solid rafi'inate and the washeds M Ir t 24 3 4 5 1 2 solid residue from the extract (filtrate) forisophthalic,

o i In ma c 7 Solid msiduefmm 0mm" 9M 4'5 0 6 terephthalic andorthophthalic acids for each extraction Wash water residue 82.3 15.2 1 5V are reported in Table 1. Examples III and IV above are 49 alsoincluded in Table I.

Table I Lithium Solid raffmate, U.V. 211211., Solid residue fromextract, bromide rnol percent U.V. ana1., mol percent Example Wt. Gramspercent Wt.,g. I.A.1 T.A.2 0A.! Wt,g LA. T.A. 0.1L

in acetone 1 Isophtlialic acid. 2 Tcrcphthalic acid. 3 Grthophthalicacid.

EXAMPLE IV As an example employing purification of the solid residuefrom the extract, a solution of 2 g. of dried lithium From the data ofTable I, it is apparent that as the amount of lithium bromide in a givenamount of solvent was increased, the yield of residue from the extractwas proportionately increased and the yield of solid rafiinate wasdecreased. The increase in soluble acid in the extract was found to holdtrue until lithium bromide concentration was raised to about 25 weightpercent where the rate of increase fell off and in one instance actuallyshowed a decrease in soluble acids at 25 weight percent lithium bromide.Further, with increased lithium bromide, the purity of isophthalic acidin the residueiirorn the extract is slightly decreased and the purity ofthe terephthalic acid in the solid rafiinate is substantially increased.

solution as indicated in Table II.

EXAMPLES X TO XII Separations in accordance herewith were made usingvarying amounts of acetone solvent in the lithium bromide In eachseparation, 2.0 g. of a 50-50 mixture of the isophthalic andterephthalic acid were mixed with 1.0 gram of lithium bromide and theamount of solvent indicated. The mixtures were allowed to stand forabout 30 minutes at room temperature and then filtered. The filtrate ofeach was evaporated to remove the acetone and then was washed with ml.of water and filtered to remove lithium bromide in the wash Water. Theremaining solid residue from the extract (filtrate) was analyzed(ultraviolet) with the results reported in Table II.

The data of Table II, above, indicates that although increasing theamount of solvent used may slightly increase The data of Table IIIdemonstrate that mixtures of acids having various ratios of isophthalicto terephthalic acid may be separated by this invention. With regard tothe above data, a comparison of Examples XV and XVII to XX indicatesthat increased yield is obtained with increased weight percent oflithium bromide in the solvent, although selectivity for the isophthalicisomer decreases slightly with increased yield. Further, in comparingExamples XVIII and XXI, increased total amount of lithium bromide andsolvent gave better selectivity.

Further experiments on the separation were carried out by repeating theprocedure of Example III at 0 and C. The results from these experimentsindicated an extract (dissolved acid) yield advantage at highertemperatures and a slight increase in selectivity in the extract atlower temperatures. Conversely, at lower temperatures, the yield ofraffinate insoluble acid increased and at higher temperatures, increasedpurity of terephthalic acid in the raflinate was obtained.

EXAMPLES XXII AND XXIII To determine the eilect of the dryness oflithium bromide, the procedure of Example II was repeated using 2.0grams of lithium bromide in 30 ml. of acetone with 2.0 grams of the50-50 mixture of acids. In one run (Example XXIII) the lithium bromidewas not dried prior to mixing with acetone. The results are reported inTable IV.

Table IV Solid raifinate, U.V. anal., Solid residue from extract,

mol percent U.V. anaL, mol percent Example Lithium bromide Wt., g. LA.I.A O.A Wt., g. LA. T.A. O.A.

XXII Dried 1.15 3. 3 96. 7 1.1 89. 9 8. 9 1. 2 XXIII Not dried 1.2 17.182.7 0.2 0.8 92.1 7.1 0.8

the total yield of dissolved acid, no appreciable change in selectivityoccurred. It is concluded that it is necessary to use only that amountof solvent which will solubilize the lithium bromide.

EXAMPLES XIII TO XXI In accordance with this invention, separations bythe procedure of Example III were carried out varying the Referring tothe data of Table IV, the dried lithium bromide increased the totalextract obtained and more completely removed isophthalic acid from theraflinate leaving a higher purity terephthalic acid in the rafiinate.

In order to demonstrate the procedure for determining a suitableoxygen-containing organic solvent, the solubility of 1 gram of lithiumbromide in 15 ml. of each of various proposed solvents was determined.The lithium bromide was dried in a vacuum oven at C. for 24 hours. The 1gram of anhydrous lithium bromide was added to the 15 ml. of eachsolvent and the solvent was then warmed to boiling and agitated for 3hours while Table III Lithium bromide Feed Solid raflfinatc Solidresidue from extract t Acle/gpne, Exam 1e W p Wt., g. percent (grams)Wt., g. IAzTA Wt., g. LA. T.A. O.A. Wt, g. LA. 'I.A. O.A.

m V acetone 2. 16. 7 15 12 1. 5 211 0. 6018 97. 1 2. 9 2. 8 16. 7 15E12; 2. 5 4: 1 0. 7342 92. 5 6. 3 1.2 2. O 16. 7 15 (12) 3. 5 6:1 0.667395. 5 3. 9 0. 6 2. 0 8. 3 30(24) 3.0 9:1 0. 8421 92. 9 6. 4 0.7 0. 54.15 15(12) 3. 5 6:1 .3 19. 0. 2222 92.0 7.0 1. 0 1. 0 8. 3 (12) 3. 56:1 0 20. 0. 4545 92.0 7.6 0. 4 l. 5 12. 5 15(12) 3. 5 6:1 .9 20. 6 0.6292.3 7. 7 0.0 3. 0 25.0 15(12) 3. 5 6:1 2.06 75. 9 23. 9 0.2 1. 14 91. 67. 7 0. 7 2. 0 v 8. 3 30 (24) 3. 5 6:1 2. 5194 1 0. 4273 95. 7 2. 2 2.1

1 An additional 0.4515 gram containing 86.5 Weight percent I.A., 12.2weight percent I.A and 1.3 weight water used to wash the extract residueby evaporating the wash water to about 20 1111., cooling and filtering.

percent O.A. was recovered from the wash cooling to 25 C. Anyundissolved lithium bromide was noted. The results were as follows:

Solvent Solubility Ethanol Soluble.

Isopropanol Mostly soluble, small amount insoluble.

n-Butanol Soluble.

Methyl ethyl ketone Mostly soluble, trace insoluble.

Ethylene glycol monocthyl ether acetate Soluble.

Ethyl acetate Mostly soluble, very small amount insoluble.

Ethylene glycol monoethyl ether Soluble.

S-pentanone Soluble.

5 Soluble hot, but on cooling a small amount came out of solution.

The above solvents all exhibited sufiicien't solubility so that they maybe used in this invention. Other solvents may readily be determined bythose skilled in the art by simple experimentation.

The lithium bromide may also be used to increase the efficiency ofsolvents which selectively or preferentially dissolve isophthalic acidand reject the terephthalic isomer as a solid. For example, in employingtertiary amines or pyridines such as 4-methyl pyridine for the selectiveseparation of mixtures of the acid isomers, lithium bromide may be addedto the extraction mixture as an auxiliary separating agent in amounts ofat least about 2 Weight percent and preferably about weight percentbased on the solvent. The lithium bromide, however, must be sufficientlysoluble in the solvent with which it is used to provide an amount oflithium bromide in the extraction system sufficient for effectiveenhancement of se lectivity of the solvent.

Although we do not intend to be held by any theories regarding theseparation phenomena of lithium bromide in separating isophthalic andterephthalic acids, we believe that the lithium bromide forms a complexwith the isophthalic acid, which complex is soluble in the sameoxygenated organic solvent which solubilizes the lithium bromide. Wehave varied the amount of lithium bromide per mol of isophthalic(soluble) acid in some of the above examples in illustration of thisinvention and from the amount of isophthalic acid solubilized We havecalculated the mol ratio of lithium bromide to soluble acid in thesoluble complex as follows:

Wt. percent M 01 ratio, Example LiBr in LiBr/soluble acetone acid XVII4.15 4.25 XVIII 8. 3 3. 8 XIX 12. 5 4. 45 XV 16. 7 4. 3 XX 1 25.0 5. 2

1 Prepared from a 6:1 IAzTA feed.

the mole ratio of lithium bromide to soluble acid in the complexremained relatively constant, as follows:

IAz-TA Wt. percent Mol ratio, Example ratio LiBr in LiBr/soluble acetoneacid Ail percentages herein indicated are percentages by Weight unlessotherwise stated.

It is evident from the foregoing that We have provided a method forseparating isomers of phthalic acid, and particularly isophthalic andterephthalic acids, using lithium bromide as a complexing agent and asolvent for a complexed isomer.

We claim:

1. A method of separating isophthalic acid from a normally solid acidmixture of isophthalic acid with terephthalic acid, which methodcomprises treating said mixture at a temperature in the range of fromabout -2G C. to about 160 C. with a solution of from about 1 to about 30Weight percent lithium bromide in an organic solvent containing onlycarbon, hydrogen and oxygen to produce an isophthalic acid complex, saidsolvent being selected from the group consisting of alcohols, ethers andketones in an amount sufficient to provide at least about 4 moles oflithium bromide .per mole of isophthalic acid and separately recoveringa solid ramnate phase contain ing an increased proportionate amount ofterephthalic acid and a liquid extract phase containing an increasedproportionate amount of isophthalic acid complex.

2. A method for separating isophthalic acid from a normally solid acidmixture containing isophthalic acid and terephthalic acid, which methodcomprises treating said mixture at a temperature in the range of fromabout -20 C. to about C. With a solution of from about one to about 30Weight percent of lithium bromide in an organic solvent containing onlycarbon, hydrogen and oxygen to produce an isophthalic acid complex, saidsolvent being selected from the group consisting of alcohols, ethers andketones in an amount sufficient to provide at least about 4 moles oflithium bromide per mole of isophthalic acid in said mixture, separatingthe resultant liquid extract phase containing an increased proportionateamount of isophthalic acid complex from the resultant solid rafinatephase containing an increased proportionate amount of terephthalic acid,distilling said liquid extract phase, and extracting the resultingresidue with Water.

3. The method of claim 2 wherein the lithium bromide is anhydrouslithium bromide, the organic: solvent is used in an amount of at leastabout 60 weight percent based on soluble acid in said mixture, theamount of lithium bromide is in the range of from about 10 to about 30Weight percent based on the organic solvent, and the treatingtemperature is in the range of from about 0 C. to about 40 C.

References Cited in the file of this patent UNITED STATES PATENTS2,833,816 Saifer et al May 6, 1958 2,840,604 Feighner et. a1 June 24,1958 2,857,429 Brunson et al Oct. 21, 1958

1. A METHOD OF SEPARATING ISOPHTHALIC ACID FROM A NORMALLY SOLID ACIDMIXTURE OF ISOPHTHALIC ACID WITH TEREPHTHALIC ACID, WHICH METHODCOMPRISES TREATING SAID MIXTURE AT A TEMPERATURE IN THE RANGE OF FROMABOUT -20* C. TO ABOUT 100*C. WITH A SOLUTION FROM ABOUT 1 TO ABOUT 30WEIGHT PERCENT LITHIUM BROMIDE IN AN ORGANIC SOLVENT CONTAINING ONLYCARBON, HYDROGEN AND OXYGEN TO PRODUCE AN ISOPHTHALIC ACID COMPLEX, SAIDSOLVENT BEING SELECTED FROM THE GROUP CONSISTING OF ALCHOLS, ETHERS ANDKETONES IN AN AMOUNT SUFFICIENT TO PROVIDE AT LEAST ABOUT 4 MOLES OFLITHIUM BROMIDE PER MOLE OF ISOPHTHALIC ACID AND SEPARATELY RECOVERING ASOLID REAFFINATE PHASE CONTAINING AN INCREASED PROPORTIONATE AMOUNT OFTEREPHTHALIC ACID AND A LIQUID EXTRACT PHASE CONTAINING AN INCREASEDPROPORTIONATE AMOUNT OF ISOPHTHALIC ACID COMPLEX.